Method for Maintaining Register Integrity and Receive Packet Protection During Ulpi PHY to Link Bus Transactions

1. A system comprising: an interface; a transmitter/receiver coupled to the interface; and a storage array coupled to the interface; wherein the transmitter/receiver is operable to: receive commands and data over the interface; transmit and/or receive control signals over the interface; decode the received commands to identify the received commands; monitor a write sequence whenever a respective one of the received commands is identified as a write command targeting the storage array, wherein the write sequence is initiated by the identified write command; discard the identified write command when a ULPI DIR signal issued by the transmitter/receiver is asserted before the end of a predetermined period of observation during the write sequence; and allow the write sequence to complete when a ULPI STP signal received by the transmitter/receiver and the ULPI DIR signal are not asserted before the end of the predetermined period of observation during the write sequence; wherein the predetermined period of observation is shorter than the duration of the write sequence.

2. The system of claim 1 , wherein in monitoring the write sequence the transmitter/receiver is further operable to discard the write command when the ULPI STP signal is asserted during the write sequence.

3. The system of claim 1 , wherein the interface comprises a bi-directional data bus and a plurality of control signal lines; wherein the control signals are transmitted and received over the control signal lines; and wherein the commands and the data are transmitted and received over the data bus.

4. The system of claim 1 , wherein the transmitter/receiver is a USB transmitter/receiver, and the storage array is a register array.

5. The system of claim 1 further comprising a peripheral device, wherein the write command is issued by the peripheral device.

6. The system of claim 5 , wherein the peripheral device is a ULPI LINK device.

7. The system of claim 1 , wherein the transmitter/receiver comprises an FSM (Finite State Machine) and wherein said monitoring the write sequence is performed through the FSM.

8. The system of claim 7 , wherein the FSM comprises: a Register Write Idle state; a Register Write Data state; and a Register Write Complete state.

9. The system of claim 8 , wherein in discarding the write command, the FSM transitions from the Register Write Data state to the Register Write Idle state.

10. The system of claim 8 , wherein in allowing the write sequence to complete, the FSM transitions from the Register Write Data state to the Register Write Complete state.

11. The system of claim 8 , wherein in allowing the write sequence to complete, the FSM transitions from the Register Write Data state to the Register Write Complete state, then transitions from the Register Write Complete state to the Register Write Idle state.

12. The system of claim 1 , wherein the system is a ULPI PHY.

13. A method for protecting a register write operation, the method comprising: receiving a command; decoding the command and in response to said decoding identifying the command as a write command initiating a register write sequence; generating a ULPI DIR signal; receiving a ULPI STP signal; and monitoring the register write sequence initiated by the write command, said monitoring comprising: discarding the write command when the ULPI DIR signal is asserted before the end of a predetermined period of observation during the register write sequence; and allowing the register write sequence to complete when a ULPI DIR signal and the ULPI STP signal are not asserted before the end of the predetermined period of observation during the register write sequence; wherein the predetermined period of observation is shorter than the duration of the write sequence.

14. The method of claim 13 , wherein said monitoring further comprises discarding the write command when the ULPI STP signal is asserted during the register write sequence.

15. The method of claim 13 , wherein said receiving is performed over a data bus; and wherein the ULPI DIR signal is indicative of a direction of signals traveling over the data bus.

16. The method of claim 13 further comprising receiving data over a data bus, wherein the write command is comprised in the data received over the data bus.

17. The method of claim 13 further comprising transmitting signals over a signal bus, wherein the ULPI DIR signal is one of the signals transmitted over the signal bus.

18. The method of claim 13 further comprising receiving signals over a signal bus, wherein the ULPI STP signal is one of the signals received over the signal bus.

19. The method of claim 13 , wherein said monitoring is performed through an FSM.

20. A USB system comprising: a data bus; a signal bus; a USB transmitter/receiver coupled to the data bus and to the signal bus; a register array coupled to the data bus; and a ULPI LINK device coupled to the data bus and to the signal bus; wherein the USB transmitter/receiver is operable to: receive commands from the ULPI LINK device over the data bus; decode the received commands to identify the received commands; monitor a register write sequence whenever a respective one of the received commands is identified as a register write command targeting the register array, wherein the register write sequence is initiated by the identified register write command; discard the identified register write command when a ULPI DIR signal issued by the USB transmitter/receiver is asserted before the end of a predetermined period of observation during the register write sequence; and allow the write sequence to complete when a ULPI STP signal received by the USB transmitter/receiver and the ULPI DIR signal are not asserted before the end of the predetermined period of observation during the register write sequence; wherein the predetermined period of observation is shorter than the duration of the write sequence.

21. The system of claim 20 , wherein in monitoring the register write sequence, the USB transmitter/receiver is further operable to discard the register write command when the ULPI STP signal received by the USB transmitter/receiver is asserted during the register write sequence.

22. The system of claim 20 , wherein the USB transmitter/receiver comprises an FSM (Finite State Machine), and wherein said monitoring the register write sequence is performed through the FSM.

23. The system of claim 22 , wherein the FSM comprises: a Register Write Idle state; a Register Write Data state; and a Register Write Complete state.

24. The system of claim 23 , wherein in discarding the register write command, the FSM transitions from the Register Write Data state to the Register Write Idle state.

25. The system of claim 23 , wherein in allowing the register write sequence to complete, the FSM transitions from the Register Write Data state to the Register Write Complete state.

26. The system of claim 23 , wherein in allowing the register write sequence to complete, the FSM transitions from the Register Write Data state to the Register Write Complete state, then transitions from the Register Write Complete state to the Register Write Idle state.